move tests to corresponding folder

tests/image/test_situ_image.py

@@ -0,0 +1,22 @@
+from situr.image import extend_dim, remove_dim
+
+import numpy as np
+import unittest
+
+
+class TestDimMethods(unittest.TestCase):
+    def test_identical_after_expand_remove_(self):
+        arr = np.random.rand(5, 2)
+        self.assertTrue(
+            np.array_equal(
+                arr, remove_dim(extend_dim(np.copy(arr)))
+            )
+        )
+
+    def test_extend_dim_only_extends(self):
+        arr = np.random.rand(5, 2)
+        self.assertTrue(
+            np.array_equal(
+                arr, extend_dim(np.copy(arr))[:, :-1]
+            )
+        )